1. Field of the Invention
The present invention relates to a technique for enabling exchange of communication media to be utilized during communication smoothly without interrupting communication.
2. Description of the Background Art
Conventionally, a technique for carrying out exchange of communication media by guaranteeing an order of packets during communication has not been considered in a system in which the communication is to be continued while appropriately exchanging mutually different communication networks according to various conditions.
As a method for guaranteeing an order of packets in general, an example in the case of cellular phone system is shown in FIG. 1, where the closest base station changes as A, B, C in conjunction with a move of the cellular phone. Here, it is assumed that initially packets are reaching from a base station A to the cellular phone. The cellular phone moves while carrying out communication, and the closest base station is changed to B. At this point, the order of packets is guaranteed as packets are transferred from the base station A to the base station B. Moreover, in the case where the cellular phone moves and the closest base station is changed to C, the order is guaranteed as packets are successively transferred from the base station A to the base station B, and from the base station B to the base station C. This method certainly can guarantee the order of packets, but this method also causes a waste in the communication path in conjunction with a move of the cellular phone, so that this method is going to consume communication facilities wastefully.
On the other hand, as a technique capable of exchanging communication media during communication, the Mobile IP is known, but the exchange of communication media that guarantees the packet order has not been considered in the Mobile IP, and the processing of an upper layer than the IP layer is held responsible for guaranteeing the packet order in the Mobile IP.
Now, when it becomes possible to simultaneously establish two communication paths using different communication media, at a time of exchanging the communication media to be utilized during communication, it becomes necessary to guarantee the order of packets that are being exchanged and to carry out the exchange at a timing where no packets exist on communication paths between hosts that are carrying out the communication, in order to continue the communication smoothly even after the communication media to be utilized are exchanged.
It is therefore an object of the present invention to provide a communication scheme capable of guaranteeing the order of packets to be exchanged in the communication while carrying out the exchange of communication media to be utilized at a timing where no packets exist on communication paths between communicating hosts, so as to be able to continue the communication smoothly even after the communication media to be utilized are exchanged.
According to one aspect of the present invention there is provided a method for exchanging communication media during a communication between a source host and a destination host in a communication system, the method comprising the steps of: (a) establishing a second communication path using a new communication medium to which the communication is to be exchanged between the source host and the destination host while carrying out the communication through a first communication path using an original communication medium; (b) transmitting from the source host to the destination host a first check packet through the first communication path, and stopping transmission of user data packets from the source host upon transmitting the first check packet; (c) transmitting from the destination host to the source host the first check packet through the second communication path upon receiving the first check packet through the first communication path while transmitting a second check packet through the first communication path, and stopping transmission of user data packets from the destination host upon transmitting the second check packet; (d) transmitting from the source host to the destination host the second check packet through the second communication path upon receiving the second check packet through the first communication path; (e) starting transmission of user data packets from the source host to the destination host through the second communication path upon receiving the first check packet through the second communication path; (f) starting transmission of user data packets from the destination host to the source host through the second communication path upon receiving the second check packet through the second communication path; and (g) disconnecting the first communication path between the source host and the destination host when the communication through the second communication path is started.
According to another aspect of the present invention there is provided a host device for carrying out a communication while exchanging communication media in a communication system, the host device comprising: a communication path management unit for establishing a second communication path using a new communication medium to which the communication is to be exchanged between the host device and a correspondent host while carrying out the communication through a first communication path using an original communication medium, and disconnecting the first communication path between the host device and the correspondent host when the communication through the second communication path is started; and a check packet processing unit for transmitting a first check packet through the first communication path to the correspondent host and stopping transmission of user data packets from the host device upon transmitting the first check packet, while transmitting a second check packet through the second communication path to the correspondent host upon receiving the second check packet through the first communication path from the correspondent host, and starting transmission of user data packets through the second communication path to the correspondent host upon receiving the first check packet through the second communication path from the correspondent host.
According to another aspect of the present invention there is provided a host device for carrying out a communication while exchanging communication media in a communication system, the host device comprising: a communication path management unit for establishing a second communication path using a new communication medium to which the communication is to be exchanged between the host device and a correspondent host while carrying out the communication through a first communication path using an original communication medium, and disconnecting the first communication path between the host device and the correspondent host when the communication through the second communication path is started; and a check packet processing unit for transmitting a first check packet through the second communication path to the correspondent host upon receiving the first check packet through the first communication path from the correspondent host while transmitting a second check packet through the first communication path to the correspondent host, stopping transmission of user data packets from the host device upon transmitting the second check packet, and starting transmission of user data packets through the second communication path to the correspondent host upon receiving the second check packet through the second communication path from the correspondent host.
Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.